1. Magnetic Head Suspension Assemblies
Computer disc drives store information on rotating magnetically recordable discs. This information is stored in concentric tracks on the rotating disc. A magnetic head or transducer element is moved from track-to-track on these discs to read and record the desired information. Typically, these rotating discs are closely held apart in a parallel stacked relationship. Sometimes, however, only one rotating disc is found in the disc drive. In either case, available vertical space is very limited in the construction of the disc drive. Accordingly, these magnetic heads or transducer elements must be designed to be held in close contact with a rotating disc or between two very closely spaced apart parallel rotating discs. Magnetic head suspension assemblies provide an arm-like structure which is inserted either above a single rotating disc or between two separately spaced apart rotating discs, moving the magnetic head back and forth. These suspension assemblies support the magnetic head which is held near the surface of the disc as the disc rotates. This magnetic head is carried in a carrier or slider which is pushed gently against the surface of the disc when the disc is not rotating by the suspension assembly. When the disc begins to rotate at high speed, the slider is aerodynamically shaped to fly slightly above or very slightly away from the surface of this rotating disc. When the slider flies slightly away from the rotating disc, the magnetic head contained in the slider is then moved back and forth from track to track by the action of the support assembly holding the slider. In certain disc drive designs, the carrier of this magnetic head rides on a liquid film on the rotating disc. In either the air or liquid case, the magnetic head suspension assembly connects the slider to a rotary or linear actuator which operates to move the suspension assembly thereby positioning the magnetic head or transducer element directly above the desired track location on the disc. Acting as an arm, the suspension assembly also provides a point support for the slider which allows the slider to gimbal in order to adjust its orientation as appropriate to the surface of the disc. Typically, in many disc drives, a plurality of magnetic head suspension assemblies are used, each holding a magnetic head, with each magnetic head being kept in close proximity to a rotating disc, thereby requiring a plurality of parallel suspension assemblies, with each suspension assembly extending between two very closely spaced apart parallel rotating discs.
Magnetic head suspension assemblies typically are composed of an elongated load beam adapted to be connected to an actuator arm at one end. At the other end, an arrangement of flexible members, or flexure is provided. To this flexure is attached the slider which carries the magnetic head. This flexure is designed to allow limited up-and-down spring-type movement in the slider which is holding the magnetic head or transducer. A point for this slider to be mounted to and gimbal about is provided at this flexure.
As disc drives have become smaller in size with increased data storage capacity, data recording density of the disc has gone up dramatically and the data tracks have become smaller and closer together. The magnetic heads and sliders have also decreased in size. These lighter weight magnetic heads and accompanying sliders require a flexible suspension to support them as the older suspensions tended to be too stiff to allow the new smaller sliders to adjust their position. In addition, while the suspension assembly must be flexible in the vertical direction as well as allow for some pitch and roll of the slider, the suspension also must be rigid in the horizontal or lateral direction in order to prevent unwanted side-to-side yaw movement in the slider. Traditionally, this problem was solved by using thinner and thinner suspension assemblies with a proportionally larger ratio of width-to-thickness. However, the lower limits of the thickness to which materials can be milled are being approached. Steel can be milled accurately to a thickness of 0.025 millimeters. In attempting to mill steel to such a small thickness, the irregularities in the grain structure of the steel can cause great variations in the thickness and make material unsuitable for use in suspension assemblies. As such, the desire exists for a new method or material which can be used to produce thinner suspension assemblies, overcoming the problems inherent in steel suspension assembly fabrication at this exceptional thinness.
Another issue encountered in the present design of magnetic head suspension assemblies is that the trend in the industry has been to design concentric tracks closer and closer together. As these tracks become closer and closer together, it becomes more difficult for current suspension assemblies to find and follow a particular track. A novel suspension assembly design would be to place a microactuator on the suspension near the slider as a way of providing small, fine tuned track following capabilities while a main rotary actuator provides the large actuation motions. These micro-actuators can be magnetically driven or electro-statically driven.
In the construction of magnetic head suspension assemblies, it is also necessary to provide a downward vertical loading force acting from the load beam through the flexure and onto the slider which holds the magnetic head against the rotating disc. This downward vertical force is counterbalanced by the lifting force when the slider flies above the rotating disc drive. (It is to be understood that if a slider is instead positioned below a rotating disc, the vertical force will instead be directed upwards). The balancing of the loading and lifting forces is stabilized when the slider positions the magnetic head very close, but not touching, the rotating disc. In order to have the magnetic head closely follow the disc surface at constant spacing, it is desirable to enable the slider to roll around a first axis substantially parallel to the load beam of the suspension assembly and to pitch about a second axis orthogonal to the first axis. It is also desirable to eliminate yaw about an axis substantially parallel to said first axis.
As it is necessary to have the magnetic head in electrical communication with various control circuitry located elsewhere in the disc drive, all prior art designs have used some form of wire which is attached to the magnetic head and strung along the load beam of the suspension assembly. This wire may be glued to the load beam. Minimizing the amount of wiring along the load beam, especially at the connection point to the slider holding the magnetic head would be desired as a further space saving measure. Present systems which use pre-amp circuits require that these components be placed some distance away from the magnetic head as they are too heavy and bulky to be carried on the suspension assembly, where available space is extremely limited. A system for placing these components closer to the magnetic head, and decreasing their bulk and weight in the system would be highly desirable. In addition, the possibility of integrating electrical leads, pre-amp circuitry, and a microactuator device into a suspension assembly would offer the advantages of a reduced number of components, simplified assembly, and higher performance.
Consequently, the need exists for an exceptionally thin magnetic head suspension assembly which is enabled to reach between two parallel closely spaced stacked rotating discs or above a single rotating disc, where minimal space is available. In spite of its exceptional thinness, however, this magnetic head suspension assembly must be sufficiently rigid to resist any unwanted bending yaw motion, and also provide a stiff enough load beam which provides and carries a downward (or upward) vertical load through to the slider holding the magnetic head, thus tending to hold the slider in position against the disc. In addition, the preferred suspension assembly must have a high resonance frequency to avoid unwanted vibrations and must also maintain pitch and roll gimbal stiffness for its slider which is comparable to present designs. In addition, the need exists to minimize the size and weight of electrical components and wiring connections along the load beam. The desired end result of this design would be fabricating miniaturized electrical leads connecting directly with the slider, with a miniaturized pre-amp circuit and a microactuator also being directly fabricated onto the load beam thereby providing a compact integrated device.
Accordingly, a novel approach to solving the above limitations would be to fabricate the entire suspension assembly from a silicon structure, for example a silicon crystal wafer. This would enable manufacture of a very thin suspension assembly which could be etched away to a very small thickness using processing methods similar to those presently used in the integrated circuit fabrication industry. An etched silicon suspension assembly would be sufficiently rigid and the various electrical components, such as leads running directly to the magnetic head, a pre-amp circuit and a microactuator could be etched directly on the silicon load beam, thus providing an extremely thin and compact system.
2. Specific Prior Art Systems
U.S. Pat. No. 3,931,641 to Watrous discloses a transducer suspension mount apparatus. This device provided a head arm assembly which is responsive to changes in the topography of the surface of a spinning disc, thereby maintaining a substantially uniform close distance and attitude between the magnetic head transducing gap and the rotating disc surface. This head suspension assembly is designed to respond with pitch and roll movements in its transducer carrier while resisting against any radial, circumferential and yaw motions. This device suffers from various limitations. First, it does not possess the required extreme thinness as needed in today's magnetic head suspension assemblies. This is due in particular to the fact that Watrous' load beam has a plurality of flanges giving rigidity to its structure, but also thickening it. Secondly, as the Watrous design is not fabricated from silicon, there is no capacity to fabricate electrical leads to the slider, a pre-amp circuit, or a microactuator directly into the load beam.
U.S. Pat. No. 4,953,834 to Ebert et al. discloses a bending spring joint formed of a selectively etched silicon wafer material. This joint is designed for use in flexible suspensions for pendulums, having a generally T-shaped pendulum and a pendulum fastening device. The Ebert system is not structured or adapted to be used as a magnetic head suspension assembly.
U.S. Pat. No. 5,006,946 to Matsuzaki discloses a flexible polymeric resonance magnetic head supporting device. This device provides a magnetic head supporting device with a reduced size and simple wiring structure. This device suffers from various limitations. First, the load beam of this head supporting device is not very thin. The thickness of this load beam is partially due to the fact that the supporting arm comprises a resilient spring portion and a rigid beam portion contiguous to said resilient spring portion, thus giving added thickness to the support arm suspension assembly. This rigid beam portion is also provided on both sides with flanges which also contribute to the thickness of the support suspension assembly. As this suspension assembly is not made of silicon, it is not possible to have electrical leads, a pre-amp circuit, or a microactuator integrated directly into the load beam of the suspension assembly.
U.S. Pat. No. 5,124,864 to Matsuzaki discloses a magnetic head supporting device including a flexible member of polymeric resonance material. This device assures an appropriate balance between the dynamic pressure for lifting the magnetic head from the rotating disc and the spring pressure exerted by the supporting device, thus achieving a stable floating posture for an accompanying slider. The Matsuzaki device suffers from various limitations. As this device is not fabricated from silicon, the Matsuzaki magnetic head supporting device will not be extremely thin and will not be adapted such that electrical leads to the slider, a pre-amp circuit, or a microactuator could be directly fabricated on the magnetic head supporting arm or suspension assembly.
U.S. Pat. No. 5,353,181 to Frater, et al. discloses an etched suspension system. This head suspension assembly comprises a load beam, a flexure, and a transducer assembly. This suspension system suffers from various limitations. First, it is rather thick. This is caused in part by the fact that the load beam has flanged sides and that the flexure is mounted adjacent to the load beam along a significant portion of this load beam. Secondly, as this suspension system is not adapted to be manufactured from silicon, the advantages of exceptional thinness and the potential for fabricating electrical leads, a pre-amp circuit, and a microactuator directly on the load beam of the suspension assembly, cannot be met.